The present invention relates to a silent chain suitable for use in a timing chain power transmission system for automobiles, a chain power transmission system for industrial machinery, and so on.
Conventionally, a silent chain used extensively for power transmission between a crankshaft and a camshaft of an automobile engine is comprised of a large number of interleaved link plates each having a pair of link teeth formed into a bifurcated configuration for mesh with teeth of a sprocket. When the silent chain is in a stretched substantially straight state, an inside meshing surface (inside flank) of each link tooth of one link plate projects slightly outward from an outside meshing surface (outside flank) of laterally overlapping one tooth of the adjacent link plate. With this arrangement, the inside meshing surfaces (inside flanks) of the link plates contact the teeth of the sprocket at the beginning of engagement with the sprocket, and the outside meshing surfaces (outside flanks) of the link plates contact the teeth of the sprocket when the silent chain wraps around the sprocket. In this manner, the contact between the link plates and the sprocket occurs in two steps to reduce the noise during power transmitting operation.
In a conventional silent chain disclosed in Japanese Patent Publication No. (HEI) 2-19339, each link tooth has an arcuate inside meshing surface so profiled as to secure sliding contact with teeth of a sprocket to avoid generation of striking sound when the silent chain starts to mesh with, or leaves from, the sprocket.
In another conventional silent chain disclosed in Japanese Patent Laid-open Publication No. (HEI) 8-74940, each link tooth has an arcuate inside meshing surface whose radius of curvature is set to approximately twice or larger than the chain pitch. During meshing engagement between the silent chain and a sprocket, the arcuate inside meshing surfaces of link plates interfere with teeth of the sprocket so as to suppress up and down motion of the silent chain with respect to the sprocket, thereby reducing the operation noise.
The conventional silent chains are able to reduce meshing sound resulting from engagement of the inside meshing surfaces of the link plates with the sprocket teeth at the start of meshing engagement between the silent chain and the sprocket. However, since the engagement proceeds interruptedly from the inside meshing surfaces to the outside meshing surfaces, additional meshing sound is produced when the outside meshing surfaces contact the sprocket teeth so as to bring the link plates in a completely seated position on the sprocket teeth.
Additionally, the arcuately profiled inside meshing surfaces of the conventional silent chains produce an elastic elongation resulting from up and down movement of the silent chain caused when the silent chain performs a power transmitting operation under stretched condition. Due to the elastic elongation, the chain is slackened at its slack side, thereby causing chordal up and down motion of the chain at the slack side thereof. The chordal up and down motion produces additional vibratory sound, which increases the total noise measured as an overall value during power transmitting operation, and makes it difficult to maintain a constant meshing point with respect to the driven sprocket located at the trailing end of a slack run of the silent chain.
It is accordingly an object of the present invention to provide a low noise silent chain which can secure smooth and continuous shifting of meshing engagement of the silent chain with a sprocket from the inside meshing surfaces of link teeth to the outside meshing surfaces of the link teeth, thereby reducing the total noise level of the chain through suppression of meshing sound between the outside meshing surfaces and teeth of the sprocket.
Another object of the present invention is to provide a low noise silent chain which is capable of suppressing vibratory sound of the chain during power transmitting operation to thereby reduce the noise level of the chain as a whole.
According to the present invention, there is provided a low noise silent chain for mesh with a sprocket, comprising: a number of link plates each having a pair of link teeth formed into a bifurcated configuration for mesh with teeth of the sprocket. The link plates are interleaved and connected together by connector pins. Each link tooth has an inside meshing surface formed on the inside flank thereof, an outside meshing surface formed on the outside flank thereof, and a tip at which the inside and outside meshing surfaces merge together. The inside meshing surface of one link tooth, when the silent chain is stretched straight, projects slightly outward from the outside meshing surface of another link tooth that overlaps the one link tooth so that the meshing engagement of the link teeth with respect to the sprocket teeth starts from the inside meshing surface and is ended when the outside meshing surface is seated on one sprocket tooth. The inside meshing surface includes a convexly arcuate mesh start portion disposed on a tip side of each link tooth, and a convexly arcuate mesh guide portion disposed on a root side of each link tooth. The convexly arcuate mesh guide portion has a radius of curvature and a circular arc length which are greater than a radius of curvature and a circular arc length, respectively, of the convexly arcuate mesh start portion.
In one preferred form of the invention, the radius of curvature and circular arc length of the convexly arcuate mesh start portion are made irregular between link plates arranged in the longitudinal direction of the silent chain.
It is desirable that the inside meshing surface is profiled such that the inside meshing surface can maintain smooth slide contact with the tooth flank of one sprocket tooth throughout a region extending from the convexly arcuate mesh start portion to the convexly arcuate mesh guide portion. The convexly arcuate mesh start portion and the convexly arcuate mesh guide portion may be directly connected together to form the inside meshing surface. As an alternative, the inside meshing surface may further include an intermediate portion disposed between the convexly arcuate mesh start portion and the convexly arcuate mesh guide portion. The intermediate portion may have a convexly arcuate profile having a radius of curvature different from those of said convexly arcuate mesh start portion and said convexly arcuate mesh guide portion. Alternatively, the intermediate portion may have a rectilinear profile.
In the low noise silent chain, since the meshing proceeds smoothly and continuously from the arcuate mesh guide portion of the inside meshing surface of one link plate to the outside meshing surface of the preceding link plate, a clearance formed between the arcuate mesh guide portion of the link plate and the tooth flank of the sprocket tooth when the link plate seated on the sprocket tooth flank can be minimized. In the case of a sprocket having a maximum number of teeth, the clearance can be reduced to approximately zero.
Teeth of the sprocket used with the low noise silent chain have an involute tooth form. The silent chain can be used in combination with sprockets having any other tooth form than the involute tooth form.
When the silent chain of the present invention engages the sprocket, the inside meshing surface of a leading link tooth of one link plate contacts the tooth flank of one sprocket tooth. In this instance, since the inside meshing surface is formed at least by a convexly arcuate mesh start portion disposed on a tooth tip side and a convexly arcuate mesh guide portion disposed on a tooth root side, the sprocket tooth flank first contacts the arcuate mesh start portion, then slides on the mesh start portion, and subsequently moves into sliding contact with the arcuate mesh guide portion in an uninterrupted manner.
Because the circular arc length of the arcuate mesh guide portion is greater than that of the arcuate mesh start portion, the mesh guide portion can retain a longer engagement time than the mesh start portion. Additionally, since the radius of curvature of the arcuate mesh guide portion is greater than that of the arcuate mesh start portion, the arcuate mesh guide portion can engage the sprocket tooth flank at a smaller sliding angle than the arcuate mesh start portion. With this arrangement, one link plate gradually turns about the connector pin and is thus wrapped around the sprocket while its arcuate mesh guide portion is in slide contact with the tooth flank of one sprocket tooth. During that time, the inside meshing surface of the next following link comes into contact with the tooth flank of the next following sprocket tooth. Thus, the arcuate mesh guide portion has a concurrent slide contact guiding function, in which the respective inside meshing surfaces of two adjacent, longitudinally overlapping link plates contact the respective tooth flanks of two adjacent sprocket teeth in the same instant.
Additionally, since the circular arc length of the arcuate mesh guide portion is greater than that of the arcuate mesh start portion, the mesh guide portion can achieve smooth sliding contact with, and gradual separation from, the sprocket tooth flank. During that time, the preceding link plate gradually turns about the connector pin in such a manner as ro wrap around the sprocket. In this instance, the outside meshing surface of the trailing link tooth of the preceding link plate comes into contact with the same sprocket tooth flank, then is seated on the sprocket tooth flank. Thus, the arcuate mesh guide portion of the inside meshing surface of one link plate and the outside meshing surface of the preceding link plate concurrently make contact with the tooth flank of the same sprocket tooth at least in a moment, and thereafter, the arcuate mesh guide portion separates from the same sprocket tooth flank. The arcuate mesh guide portion also has an uninterrupted meshing guide function, in which the engagement of the arcuate mesh guide portion of one link plate with respect to one sprocket tooth is uninterruptedly taken over by the engagement of the outside meshing surface of the preceding link plate with respect to the same sprocket tooth.
By virtue of the concurrent sliding contact guiding function and uninterrupted meshing guide function of the arcuate mesh guide portion, the individual link plates of the silent chain are successively seated on the sprocket teeth to perform a power transmitting operation.
Because the arcuate mesh start portion located on a tooth tip side of the inside meshing surface of one link plate is profiled to project slightly outward from the outside meshing surface of the adjacent link plate, the working line (meshing line) of the silent chain is lifted up when the arcuate mesh start portion contacts the sprocket tooth at the start of meshing engagement between the silent chain and the sprocket. By thus lifting the meshing line, the silent chain is tensioned, so that a chain slack produced on the slack side of the silent chain can be taken up. Thus, chordal up and down motion of the chain and vibrations of the chain can be suppressed.
In the case where the radius of curvature and circular arc length of the convexly arcuate mesh start portion are made irregular between the link plates arranged in the longitudinal direction of the silent chain, the timing of meshing engagement between the arcuate mesh start portions of the individual link plates and the sprocket teeth is variable between the link plates arranged in the longitudinal direction of the silent chain. This arrangement contributes to suppression of periodic changes or fluctuations of the meshing engagement.